1. Field of the Invention
The present invention relates generally to neural stimulation, and more particularly, to determining stimulation signals for neural stimulation.
2. Related Art
Certain medical devices, sometimes referred to as tissue-stimulating prosthesis, operate by delivering an electrical stimulation to a recipient. These prostheses include, but are not limited to, cardiac pacemakers, neural stimulators, prosthetic hearing implant systems, and the like. Tissue-stimulating prostheses, which are typically reliant upon stored power, share a common dynamic. As the possible and desired functionality of the devices is improved, the power demands generally increase. As a result, the life per charge or per battery cell is reduced. This not only raises costs for the user (also referred to herein as the patient, wearer and recipient; collectively and generally referred to herein as “recipient”), it also increases the risk that a device will cease operating at an inconvenient time due to loss of power.
Prosthetic hearing implant systems, such as auditory brain stimulators and Cochlear™ implants (also commonly referred to as Cochlear™ implant devices, Cochlear™ prostheses, and the like; simply “cochlear implant” herein), are generally used to treat sensorineural hearing loss. Sensorineural hearing loss is due to the absence of, or destruction of, the hair cells in the cochlea which transduce acoustic signals into nerve impulses. Prosthetic hearing implant systems bypass the hair cells in the cochlea and directly deliver electrical stimulation to the auditory nerve fibres, thereby allowing the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered to the auditory nerve.
Prosthetic hearing systems generally include a sound processor that converts sound into a coded signal. Traditionally, during processing, a sound is decomposed into frequency bands or channels based on the “spectral power” rather than the “perceptual power” of the frequency band. The spectral power of a frequency band is the relative physical amplitude of the frequency components in the band in terms of, for example, sound pressure level. That is, the spectral power of a frequency band is an objective measure of the power level within a band. In contrast, perceptual power identifies how important a frequency component is for the perception of the sound. The traditional decomposition based on spectral power is used in current speech processing strategies of commercially available cochlear implants.
The coded signal output by the sound processor is provided to a stimulator unit situated within a recess of the temporal bone of the recipient. The stimulator unit processes the coded signal and outputs signals to an intracochlea electrode assembly which applies electrical stimulation directly to the recipient's auditory nerve, thereby producing a hearing sensation corresponding to the original detected sound.
The presence of such an electrical stimulus on one electrode may prevent or change the detection of signals delivered via other electrodes. This effect is called masking. By considering the masking effect it is therefore possible to classify signals that will not be accurately perceived by the recipient as unnecessary.